Composting is an effective waste management tool used to convert organic wastes into useful products. Various systems and methods for generating compost to improve the disposal and the beneficial re-use of organic wastes, such as garden waste, bio-solids, agricultural waste, municipal solid waste and the like, are known. Many of these systems and methods focus on the improvement of compost odor control, the rapid stabilization of compost, and the reduction of operating costs.
One type of compost generating system known in the art involves aeration. Generally, there are two different types of aeration: forced aeration and passive aeration. Forced, or fan-induced, aeration is generally utilized to provide sufficient oxygen for maintaining aerobic conditions of the microbes needed for compost generation. Forced aeration is also employed to maintain optimal temperature levels in order to reduce the production of odorous emissions. There are two basic types of forced aeration: positive and negative aeration. Composting systems that use positive aeration introduce air to the bottom of the compost pile, and the air exits the compost pile at the top of the pile. Composting systems that use negative aeration draw air from the surface of the compost pile, and the air is distributed down through an aeration floor and into an aeration network, where the odiferous air is treated to reduce its odor. Composting systems that utilize positive aeration have the disadvantage that ammonia and other odorous and/or corrosive gases are released from the surface of the compost pile. Systems that employ negative aeration usually have operational problems associated with the collection, removal and disposal of particulate matter and moisture drawn into the aeration networks.
Composting using passive aeration systems is generally carried out in large scale using turned windrow and passive heaps. However, these systems are commonly associated with significant compost odor emissions due to low oxygen levels, uncontrolled temperatures, and open compost piles.
In another type of compost generating system, the composting processes take place in enclosed structures. These enclosed systems are capable of capturing the odiferous air resulting from the composting process, which usually evolves at the surface of the compost pile. The captured odiferous air is then conveyed to a fan exhaust and treated for odor reduction before being released into the surroundings.
There are generally three different types of enclosed compost generating systems: in-vessel composting systems, in-building composting systems, and fabric-covered composting systems. In-vessel composting systems provide a sealed and insulated space for the biomass for each controlled volume of generated compost. In-building composting systems involve one or more open piles of compost stored in a single building, sharing a common headspace and sometimes intermingling biomass. Fabric-covered composting systems utilize a fabric, or film, to cover a discrete volume of compost, and can be used either in an enclosed structure or in an open area.
Three kinds of fabric or film covers are generally used in connection with fabric-covered composting systems. Macro-porous covers, such as the Compostex® brand, are constructed of a macro-porous fabric that is akin to a blanket. Macro-porous covers allow easy passage of air and can be used with composting systems that involve positive and/or negative aeration. Such covers are relatively thick, and provide moderate thermal insulation and minimal reduction of surface evaporation rates. They have the disadvantage that they do not control compost odors and are water-absorbent, and can therefore become heavy and difficult to transport.
Micro-porous covers are generally constructed of micro-porous, gas permeable, fabric and provide low air-flow rates. They can only be used with composting systems that involve positive aeration and require weighted edges to hold the covers in place as the covers tend to “balloon”, due to gas flow constriction through the fabric. The low air flow rates result in low oxygen levels and very high temperatures of the biomass. These conditions reduce the efficiency of the aerobic bacteria that generate the compost. Micro-porous covers allow minimal passage of moisture, thereby preventing drying. In addition, most of the water soluble odiferous compounds are trapped in the water under the cover and are therefore not released into the atmosphere. Further, micro-porous covers provide little thermal insulation, are quite heavy and are very expensive.
A third type of cover used with composting systems is impermeable plastic sleeves that are adapted from silage bags used to prepare and store feed for cattle. These sleeves are generally constructed of polyethylene, have a tube configuration up to about 200 feet in length, and are filled with compost by means of a special machine. The machine can also be employed to insert a perforated aeration tube into the center of the impermeable plastic sleeve. Air ports are located along the length of the aeration tube, allowing air to be drawn in and out of the impermeable plastic sleeve. However, the resulting aeration is very uneven radially about and along the axis of the sleeve. As a result, the generated compost is usually dry on top and saturated with moisture at the bottom. In order to access the compost after processing, the plastic sleeve, or tube, is slit and disposed of, and is thus not reusable. Further, foul leachate is often released onto the ground and surroundings when the plastic sleeve is removed. Compost generated using these plastic sleeves often requires significant additional processing to obtain stability.
There thus remains a need for compost generating systems and methods that overcome the aforementioned disadvantages and problems.